Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane to remove ions, molecules, and larger particles from e.g. tap water. In reverse osmosis, an applied pressure is used to overcome osmotic pressure, a colligative property, that is driven by chemical potential differences of the solvent, a thermodynamic parameter. Reverse osmosis can remove many types of dissolved and suspended species from water by retaining the solute on the pressurized side of the membrane and allowing the pure solvent to pass to the other side. The membrane is sort of selective in that large molecules or ions are not allowed through the pores (holes), but smaller components of the solution (such as solvent molecules) are allowed to pass freely.
The process of reverse osmosis can be used for the production of deionized water. Deionized water is water that has had almost all of its mineral ions removed, such as cations like sodium, calcium, iron, and copper, and anions such as chloride and sulfate. Deionization is a chemical process that uses specially manufactured ion-exchange resins, which exchange hydrogen and hydroxide ions for dissolved minerals, and then recombine to form water. Because most non-particulate water impurities are dissolved salts, deionization produces a high purity water that is generally similar to distilled water, and this process is quick and without scale buildup.
In, for example, dialysis treatment dialysis machines need deionized water to ensure correct composition of dialysis fluid. Therefore, dialysis center usually process tap water by softeners, carbon filter and a reverse osmosis processing unit. Such systems usually have a gain of just 30% and the remaining water is considered waste water (grey water) as it has been used in the system for a process or has an increased concentration of ions (mostly sodium). Reusing this fluid is uncommon due to the higher amount of diluted sodium and/or it being considered waste water as it has been used in the system.
As the processing of dialysis fluid involves high water consumption, the inventor analyzed the water consumption of the water purification system and found that only part of the input water is processed into purified water, with a high proportion and significant remainder of water being finally drained.